Scientists have made a breakthrough in studying testicular cancer in young men.
Using human tissue grafted into mice, they have been able to study the development of cells which can cause cancer.
Testicular germ cell cancer (TGCC) is the most common cancer among men aged 15 to 44 and cases are increasing.
However, testicular cancer is still relatively rare.
Experts know testicular cancer originates from the abnormal development of germ cells (cells that go on to become sex cells) in foetuses.
However, how and why this happens has been impossible to explore before now.
In the latest study, published in the journal Human Reproduction, experts formulated a new method for investigating how human testes develop in baby boys before they are born.
They took testicular tissue and grafted it into mice, watching how the cells developed normally over a six-week period.
Previous studies have not been possible because the TGCC seen in men does not occur in laboratory animals.
Testicular tissue also cannot be studied in a test tube because it does not survive and develop normally.
Using the new model, experts should be able to determine which factors interfere with development and allow cancer to develop.